I have a Denon 3802 and a Paradigm ps1000 I have had for about 7yrs. My x-over setting on my receiver is 80hz and the x-over on the sub turned all the way up using the dedicated sub out, but if I tweek the x-over on the sub from 80 to 150hz I can clearly hear the change, which I shouldn't be able to do if the receiver is clipping everything above 80hz...any ideas
Derek
Posted on
Actually the cross-over may not be exactly at 80 Hz and the 80 Hz cross-over is the -3db point. By running the cross-overs cascaded with each other, you are creating a -6db point.
Then there is the slope. If the cross-over in your receiver and sub are 12 db per octive, you are now creating a 24 db per octive slope. Most cross-overs also lower the overall volume of the sub as well.
John A.
Posted on
Derek,
"By running the cross-overs cascaded with each other, you are creating a -6db point."
Is "cascaded" where you have the two frequencies set the same e.g. 80Hz?
re slope. So topr may be hearing a - 24 dB per octave attenuation above 80 Hz with the sub cross-over at 80 Hz, and -12 dB per octave attenuation with it set at 150 Hz? That would certainly explain it.
Some of these terms are not used consistently by manufacturers, and maybe this is part of the problem in understanding what is going on. For example, the sub "Crossover" frequency is really the frequency for a -3 dB low-pass filter on the LFE channel. Is this right? If so, is that -12 dB per octave, too? Then it becomes a real crossover on speaker level connection. Is this right? And, in the former case, why do people want to limit the frequency range of the LFE ".1" channel? Dolby and DTS agree that the LFE channel can contain signal up to 120 Hz. I had a sub once that let you limit the LFE channel, even down to 40 Hz, but not change the crossover for speaker-level connections, that was set at 80 Hz. I cannot understand why it was like this, it seems completely the wrong way round.
My receiver does not have a variable "crossover", I don't know what one of those does. Mine has a fixed crossover for redirecting low frequencies from 5 channels to the sub, if that is what you choose. The manual does not say at which frequency. I prefer the sound without it, and it keeps life simpler, too...
Derek
Posted on
The primary advantage of these electronic crossovers is to reduce intermodulation distortion. Distortion is reduced during loud passages when one amp looses composure, the other is not effected - basically, this is Bi-Amping.
The -3 point is a function of the crossover. Even if it's rated at 6 db/octave, 12 db/octave, 24 db/octave, etc., that's the final slope. The frequency response isn't flat and then suddenly dives in sensitivity at the final slope. It starts to fall somewhere below the crossover frequency and makes a gentle droop until it reaches its final slope.
The -3 db point is important because the high-pass crossover for the satellites has a similar response and the -3 db point for the woofer (-3 db cuts the output in half) overlap and add to the -3 db point of the satellites for a net 0db or a flat response.
The crossovers should be set to the same crossover frequency to keep the overall response flat UNLESS: the numbers on the crossover are incorrect (more common than you think) or the speakers have a non-flat response at the crossover frequency. In that case the crossover frequencies may be different. An SPL meter or spectrum analyzer would be required to get it right though.
There are quite a few new receivers with variable crossovers these days.
I would imagine this all started in movie theatures where it was a little difficult to place decent subs at all locations (front, sides, rear etc.). Home uses do it mostly because it's cheaper [to use 5 small satelites] and because it takes up less space.
Hope this helps.
John A.
Posted on
Derek,
Thanks. Yes, it helps. But I will have to read that middle bit some more times...
Can you confirm the "crossover" setting on the sub is doing completely different things on speaker-level and line-level, and, on line-level, is not actually a "crossover" at all, just a "low-pass filter" or "HF limiter" or something. On line level are you not just blocking and throwing away frequencies above that setting (at the specified slope etc.)?
Then, if so, why does anyone want to put a limit on what they get from the LFE ".1" channel? That would be like treble-cut "tone controls" on old radios. They cut the hiss, sure, but they cut the signal, too.
Then my former sub where you could do that (for some reason) but NOT adjust the real crossover frequency to match your main speakers, which is where I can see the point of having control...
Derek
Posted on
The passive and active crossovers do the same thing - they block and absorb some sounds. The active ones are more veratile and offer lower distortion, but they cost more and are more complex to setup.
Blocking frequencies reduces interference between drivers and under certain circomstances conserves amplifier power. There's no sense in sending 20KHz signals to a 15" woofer. Though the woofer will reproduce it, the sound will be so low as to be a waste of power.
John A.
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Derek, Thanks. Keeping to the control on the sub, just so I understand, which is the passive crossover, and which is the active? Or is it just one of those? John
Derek
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Active crossovers require power and usually have variable controls. Subs have them, receivers have them and some high-end speakers have them. Active crossovers usually have RCA line-level audio inputs and/or outputs.
Paasive crossovers are capaciters and inductors (simplified) and are usually already inside the speakers. It is VERY rare for there to be any controls. No power supply is required and they usually have speaker clips or banana plugs. Almost all speakers have them. Some subs have them.
John A.
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Yes, thanks. I once made a simple passive crossover from an electronics magazine. I imagine a sub does not have one, it only has one driver.
Derek
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Some do. The kind that you run the full-bandwidth audio through and you connect your [two] satelites to pairs of spreaker clips.